Several combinations have shown positive interactions. For example, sildenafil and propionyl-L-carnitine may be more effective than sildenafil alone. Although not well studied in humans, L-carnitine used concurrently with antiviral agents such as zidovudin (Retrovir®) or carnitine used with nortryptiline may also have a positive interaction that reduces side effects. L-carnitine plus acetyl-L-carnitine plus cinnoxicam has been found more effective in improving sperm parameters as compared with L-carnitine plus acetyl-L-carnitine alone.

Patients with diabetes should use caution because L-carnitine may decrease blood sugar. However, carnitine levels did not change in diabetics using insulin or sulfonylurea therapy. It is unclear whether L-carnitine would have similar effects when combined with other medications that lower blood sugar. Consult with a qualified healthcare professional, including a pharmacist, before combining therapies.

Although not well studied in humans, carnitine may increase valproic acid concentrations in the brain, which might increase the effects of valproic acid. Caution is advised.

Interactions with Herbs and Dietary Supplements

L-carnitine may decrease the need for herbs or supplements with anticoagulant effects ("blood thinners"). L-carnitine may also decrease the need for herbs or supplements with diuretic effects. Dosing adjustments may be necessary.

Patients with diabetes should use caution because L-carnitine may decrease blood sugar. However, carnitine levels did not change in diabetics using insulin or sulfonylurea therapy. It is unclear whether L-carnitine would have similar effects when combined with other herbs and supplements that lower blood sugar. Consult with a qualified healthcare professional, including a pharmacist, before combining therapies.